The ability to accurately monitor fluids or gasses contained within processing equipment has become increasingly important in the efficient control and optimization of many industrial processes. In fluid separation applications involving the use of packed distillation or absorption columns, for example, the need to accurately monitor the temperature and concentration of fluids contained within the column may be valuable in hydrocarbon processing, solvent recycling, crude oil separation or other such applications where product quality and efficiency are important considerations. In other process applications such as the use of a bubble cap column for the distillation of fluids, the regulation of fluid height within each tray or plate may be necessary to ensure proper channeling of fluid and vapor through the column. Thus, by regulating various characteristics in the process equipment, optimization of the process can be achieved while also reducing plant costs associated with unnecessary power usage.
The monitoring of fluids or gasses in many process applications is often accomplished through the use of bulk measurements such as temperature or pressure. Typically, a wired fluid sensor is installed at the input or output of the particular process stream to be monitored, and bulk measurements are taken to establish an estimate of the process state. Depending on the particular process equipment used, installation of such sensors may be difficult or infeasible since the installation of the sensor may require the use of wire leads at prohibitive locations within the equipment or at locations otherwise incompatible with the process. In petrochemical applications involving the distillation of crude oil, for example, the elevated temperature and chemical composition of the oil may prohibit the insertion of a fluid sensor at certain locations within the process equipment. In some petrochemical applications, for example, the elevated temperature and chemical composition of the oil may prevent the installation of the sensor in the middle of the packed distillation column near the packing material. Hard-wiring of each fluid sensor within the equipment may also be cumbersome, particularly in those instances where the sensors are located far away from the control unit and/or where building codes and standards require the wires for such devices to be installed at particular locations for safety purposes.
In those cases where the use of wired fluid sensors is not prohibited, the measurements often obtained from such devices are not always representative of the actual in-situ conditions within the process since the fluid or gas may not be perfectly mixed or distributed within the process stream. This may be significant in some applications where local conditions depend on the distribution of reactants or catalysts at different points throughout the process.